1. Field of the Invention
The present invention relates to a composite member comprising a metallic sheet and a rigid synthetic resin coating. More specifically, the present invention relates to a length composite member of such as a gutter comprising a metallic sheet coated with rigid synthetic resin bent to be arcuate in transversal section or in width directional section.
2. Description of the Prior Art
In the case where a member arcuate in transversal section is fabricated only with rigid synthetic resin, such arcuate sectional member involves the shortcomings of the rigid synthetic resin per se, i.e. the shortcomings of small antishockness and liability of thermal deformation. Although such shortcomings can be overcome to some extent by selecting a material of rigid synthetic resin and the kind of an additive, the simplest and straightforward approach to that end is to increase the thickness of the arcuate sectional member. However, in consideration of the recent requirement of saving materials and energy, it is desired to provide a member of similar performance by decreasing the source material rather than simply increasing the thickness of the member. One approach which was thought of is to embed a thin metallic sheet in an arcuate sectional member made of rigid synthetic resin. More specifically, such approach fulfills the above described shortcomings of a thin rigid synthetic resin sheet by the use of a metallic sheet, while skillful use is made of anticorrosiveness, tinting power, moldability and the like which are the features of rigid synthetic resin.
In order to embed a thin metallic sheet in a rigid synthetic resin material, a preferred approach is a method of bending continuously a thin metallic sheet with several stages of forming rolls, thereby to form the same to be arcuate in transversal section with a desired curved surface and of coating both surfaces thereof with synthetic resin, inasmuch as the same can be carried out with a high production speed on a mass production basis. However, the above described method involves a problem that in the case where the thickness of a metallic sheet is extremely small as compared with the radius of curvature of the arcuate sectional member thus formed a spring back is encountered in roll forming a metallic sheet to be arcuate in section. More specifically, when a metallic sheet is bent to be arcuate in section by force and the force is removed, the sheet as deformed tends to return to the original shape due to elastic strain, thereby to cause a spring back. Therefore, in order to attain an arcuate sectional curve of a desired radius of curvature, it is necessary to bend the material in consideration of such spring back. In the case where the thickness of a metallic sheet is extremely small as compared with the radius of curvature of a desired arcuate sectional curve, it would be required to bend the metallic sheet so much as to curl the same in a cylindrical shape to lap even more than one and a half of the round. Therefore, in roll forming a metallic sheet which is extremely thin as compared with the radius of curvature of a desired arcuate sectional member to be attained, it is very difficult and becomes problematic to bend such metallic sheet. Furthermore, when such metallic sheet thus formed to be arcuate in section is coated with a rigid synthetic resin material means of extrusion molding, whereupon the same is cooled by means of a cooling means, the arcuate sectional member after cooling does not become a desired geometry (radius of curvature, width, height and the like) unless the same is cooled in consideration of a spring back of such metallic sheet, and furthermore, when heat is applied to the arcuate sectional member after cooling and the rigid synthetic resin becomes soft, the arcuate sectional member is deformed to stretch due to a spring back of the metallic sheet, with the result that the above described method still involves a disadvantage that a stabilized shape can be hardly maintained.